55 adult PKU patients (mean age 28.3 ± 6.2 years) filled out the BRIEF-A questionnaire and performed computerized tasks measuring executive functions (inhibition, cognitive flexibility, and working memory). The outcome of the BRIEF-A questionnaire was compared with the neurocognitive outcome as measured by three tasks from the Amsterdam Neuropsychological Tasks (ANT).

ANT results: 34-36% of patients showed deficits in inhibitory control; 31-24% showed deficits in cognitive flexibility, as compared to the general Dutch population.

No significant correlations between the two methods were found, which was confirmed with the Bland-Altman approach where no agreement between the two methods was observed.

The study concludes that patients reporting EF problems in daily life are not necessarily those that present with core EF deficits and that BRIEF-A is not a sufficient way to monitor EF in adult PKU patients.